Vehicle air conditioning and heating method providing engine on and engine off operation

ABSTRACT

An air conditioning system for use in an over-the-road or off road vehicle provides operation during both engine on and engine off conditions. The system includes a variable speed compressor, a motor, and a controller. The controller receives electric power from the vehicle&#39;s electric power generation system when the engine is on to enable operation of the compressor during an engine on condition. When the engine is off, the controller receives electric power from a battery to enable operation of the compressor during the engine off condition.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application is a continuation of co-pending U.S. patentapplication Ser. No. 11/088,441, filed Mar. 24, 2005, entitled “VehicleAir Conditioning and Heating System Providing Engine On And Engine OffOperation”, which is a continuation of U.S. patent application Ser. No.10/134,875, filed Apr. 29, 2002, now U.S. Pat. No. 6,889,762, the entireteachings and disclosure of which are hereby incorporated in theirentireties by reference thereto.

FIELD OF THE INVENTION

The present invention relates generally to over-the-road and off-roadvehicle air conditioning systems, and more particularly to vehiclemounted heating, ventilation, and air conditioning (HVAC) systemsutilizing variable speed motor driven compressors and controls therefor.

BACKGROUND OF THE INVENTION

The global economic expansion has stressed the transportation industry'sability to keep up with the shipping demands for raw materials andfinished products. Indeed, the demand for qualified tractor-trailerdrivers has far outstripped the ability of the industry to recruit andtrain individuals to fill the demand of the marketplace. As a result,the demand of the transportation industry to utilize the existingpersonnel and vehicles has resulted in increased time spent on the roadand in the vehicles in an attempt to meet the market demands.

In an effort to maintain the safety of the highways, federal regulationsgoverning the amount of time that a driver may spend behind the wheelhave been instituted. When such maximum times have been reached, thedriver is required to take his vehicle off the road and rest. The numberof trucks pulled over at toll plazas, weight stations, and rest stopsillustrates the compliance with such regulations. However, theselocations often do not provide anywhere for the drivers to rest,necessitating continued occupancy within the vehicle.

In response to the needs of the transportation industry and inrecognition of the locations where drivers are forced to rest,over-the-road vehicle manufacturers have continued to increase theemphasis on ergonomic factors in the design and manufacturer of theirvehicles. Indeed, the interior of a modern over-the-road vehiclecontains many features to minimize the stress and fatigue placed on thedrivers during the operation of the vehicle. These features includevibration dampers and lumbar supports in the seats, increased soundinsulation, and heating, ventilation, and air conditioning (HVAC)systems that provide a comfortable environment for the driver. Toaccommodate the required rest periods, and in recognition of theincreased usage of driving teams, which typically include twoindividuals, one who drives while the other sleeps, many over-the-roadvehicles include a sleeping compartment. This sleeping compartment isalso temperature controlled so that time spent therein provides theoccupant with a restful experience.

Unfortunately, the current state-of-the-art heating and air conditioningsystems utilize engine-belt driven compressors for the air conditioningsystem to circulate and pump the refrigerant throughout the vehicle tocool the passenger compartments. An engine-belt driven pump is alsoutilized to circulate the engine waste heat throughout the passengercompartments when heating is required. While such systems are ideallysuited to provide a temperature controlled environment during operationof the vehicle, neither of such systems is able to operate when theengine is turned off.

As a result of the inability of the current state of the art of vehicleHVAC systems to operate while the vehicle's engine is turned off, theover-the-road vehicle operators are forced to choose between two lessthan ideal situations while trying to rest. First, they may choose tocontinuously run their vehicle's engine so that they may have heating orair conditioning while they rest. Alternatively, they may choose to turnoff their engine and try to rest in a non-temperature controlledenvironment, although temperatures can often reach extremes of high andlow depending on where the vehicle happens to be when a required restperiod is reached. While the first option improves safety by providing acomfortable resting environment for the driver, it greatly increases thecost of operating the over-the-road vehicle as the engine is continuedto run, which burns additional fuel, simply to operate the heating orair conditioning system. Similarly, while the second option does notincrease the cost of operating the vehicle because the engine is turnedoff, the driver may not fully be able to rest in an environment oftemperature extremes, thus potentially reducing the safety of theoperation of the vehicle.

There exists, therefore, a need in the art for a vehicle heating,ventilation, and air conditioning (HVAC) system that is able to provideconditioning of the interior of the vehicle, not only during periods ofengine operation, but also during engine off or no-idle conditions.

BRIEF SUMMARY OF THE INVENTION

In view of the above, the present invention provides a new and improvedheating, ventilating, and air conditioning (HVAC) system for anover-the-road vehicle that may be operated regardless of the operationalstate of the engine. That is, the instant invention provides a new andimproved HVAC system that may be operated to condition the interiorcompartments of an over-the-road vehicle while the engine is running andwhile the engine is in a no-idle (off) condition.

In one embodiment to the present invention the air conditioning system'scompressor is driven by a variable-speed brushless DC motor controlledby an intelligent power generation management controller. In this way,the system can be driven from any available electrical power source,including the vehicle's electric power generation system during engineoperation, or from a storage battery, an auxiliary power unit, or shorepower during engine off or no-idle operation. The intelligent powergeneration management controller is provided to monitor the HVAC systemparameters and the operational condition of the engine to select thepower source, operating mode, and control the operational capacity forthe system. That is, under engine operating conditions the HVAC systemmay be operated at maximum capacity as supplied by the vehicle'selectric power generation system. When the engine is turned off, theintelligent power generation management controller will begin utilizinganother source of electric power to drive the variable speed motor.

This controller will modulate the operating capacity of the HVAC systembased upon the available source of power such that, for example, the airconditioning system compressor may be operated at minimum capacity whenthe only available power source is the vehicle's storage battery.Indeed, the controller also includes logic that will disable the HVACsystem when the vehicle's storage battery has been discharged apredetermined amount so that enough capacity is preserved in the storagebattery to start the vehicle and/or to limit the battery discharge levelto provide proper life the battery system.

In one embodiment of the present invention, an air conditioning systemfor use in an over-the-road vehicle is presented. This system comprisesa variable-speed compressor for providing refrigerant to a heatexchanger positioned to provide temperature control to an interiorcompartment of a vehicle. A brushless DC motor is operably coupled tothe variable-speed compressor, and an intelligent power generationmanagement controller is operably coupled to the motor. The controllerreceives electric power from at least one source of electric power thatis operable when the engine of the vehicle is not operating. Thecontroller then modulates the speed of the compressor when the engine isnot operating by varying an energization of the motor based on a powercapacity of the source. In this way, the controller enables operation ofthe compressor during an engine off condition.

Preferably, the source of electric power is a battery. In such a case,the controller operates the compressor at minimum speeds to extend aduration of operation of the air conditioning system. The controllermonitors a voltage of the battery and disables operation of thecompressor when the voltage drops below a predetermined set point. Inone embodiment the predetermined set point is set at approximately 11.5volts. Alternatively, the predetermined set point is determined by astarting power requirement of the vehicle's engine. When the source ofelectric power is shore power or auxiliary power, the controller canoperate the compressor at minimum and maximum speeds depending onperformance output requirements. In a further embodiment, the controllerreceives electric power from an engine driven electric power system andoperates the compressor at the desired speed based on performance outputrequirements.

In a preferred embodiment of the system of the present invention, thecontroller is adapted to receive electric power from a plurality ofsources of electric power operable when the engine of the vehicle is notoperating and from at least one source of electric power operable whenthe engine is operating, and wherein the controller dynamically utilizeselectric power from one of the sources based on priority logic ofavailable sources. Preferably, sources operable when the engine is notoperating include a battery, shore power, and an auxiliary power unit,and the source operable when the engine is operating is the vehicle'selectric power system. The priority logic selects the vehicle's electricpower system, the shore power, the auxiliary power unit, and thebattery, in that order, based on each of these sources availability. Inone embodiment the system also includes a heater. In this embodiment thecontroller disables the compressor and operates the heater to provideheating to the interior compartment of the vehicle when required.

In an alternate embodiment of the present invention, a heating,ventilation, and air conditioning (HVAC) system for a vehicle isprovided. This HVAC system comprises a high pressure coolant loopincluding a motor-driven compressor and a refrigerant to liquid heatexchanger, and a low pressure coolant loop in thermal communication withthe high pressure coolant loop via the refrigerant to liquid heatexchanger. The low pressure coolant loop includes a coolant pump and aliquid to air heat exchanger positioned in thermal communication with aninterior compartment of the vehicle. An intelligent power generationmanagement controller is operably coupled to the motor-drivencompressor. Advantageously, the controller receives electric power fromat least one source of electric power that is operable when an engine ofthe vehicle is not operating. The controller modulates the speed of themotor-driven compressor and operates the coolant pump when the engine isnot operating based on a power capacity of the source of electric power.In this way, the controller prolongs operation of the HVAC system duringan engine off condition when interior cooling is required.

Preferably, the low pressure coolant loop includes a coolant heater. Thecontroller can then disable operation of the compressor and operate thecoolant heater and the coolant pump when the engine is not operatingbased on a power capacity of the source of electric power to prolongoperation of the HVAC system during an engine off condition wheninterior heating is required. In an alternate embodiment of the presentinvention, a resistance type air heater is positioned in thermalcommunication with the interior compartment of the vehicle. Thecontroller then disables operation of the compressor and the coolantpump and operates the air heater when the engine is not operating basedon a power capacity of the source of electric power to prolong operationof the HVAC system during an engine off condition when interior heatingis required.

Further, the controller receives electric power from a plurality ofsources of electric power that are operable when the engine of thevehicle is not operating and at least one source of electric poweroperable when the engine of the vehicle is operating. The controllerthen selectively utilizes electric power from one of the sources basedon internal priority logic. When the source of electric power utilizedis a battery, the controller operates the compressor at a minimum speedto extend a duration of operation of the HVAC system. Preferably, thecontroller monitors the power utilization of the battery and disablesoperation of the compressor to preserve an amount of power in thebattery sufficient to start the vehicle's engine.

In a further alternate embodiment of the present invention, a heating,ventilation, and air conditioning (HVAC) system for a vehicle comprisesa high pressure coolant loop including a motor-driven compressor and arefrigerant to liquid heat exchanger, a heater, and a low pressurecoolant loop in thermal communication with the high pressure coolantloop via the refrigerant to liquid heat exchanger. The low pressurecoolant loop includes a coolant pump and a liquid to air heat exchangerpositioned in thermal communication with an interior compartment of thevehicle. An intelligent power generation management controller isoperably coupled to the motor-driven compressor, the coolant pump, andthe heater. The controller receives electric power from at least onesource of electric power that is operable when an engine of the vehicleis not operating. The controller then modulates a speed of themotor-driven compressor and operates the coolant pump when the engine isnot operating based on a power capacity of the source of electric powerto prolong operation of the HVAC system during an engine off conditionwhen interior cooling is required. Further, the controller disablesoperation of the compressor and operates the heater when the engine isnot operating based on a power capacity of the source of electric powerto prolong operation of the HVAC system during an engine off conditionwhen interior heating is required.

In one embodiment the heater is a coolant heater in thermalcommunication with the low pressure coolant loop. The controller thenoperates the coolant heater and the coolant pump when interior heatingis required. In another embodiment the heater is a resistance type orfuel fired air heater. In this embodiment the controller disablesoperation of the compressor and the coolant pump, and operates the airheater when interior heating is required.

Other features and advantages of the invention will become more apparentfrom the following detailed description when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a simplified single line block diagram illustrating coolantflow and system component interconnections in an air conditioning systemconstructed in accordance with the teachings of the present invention;

FIG. 2 illustrates an alternate embodiment of the invention forming aHVAC system capable of providing both heating and cooling of a passengercompartment of an over-the-road vehicle;

FIG. 3 is a simplified air flow diagram illustrating an alternateembodiment of an HVAC system constructed in accordance with theteachings of the present invention incorporating an air heater;

FIG. 4 is a simplified block diagram illustrating alternate power sourceutilization and compressor capacity modulation provided by theintelligent power generation management controller of an embodiment ofthe present invention;

FIG. 5 is a simplified block diagram illustrating control parameterutilization and compressor capacity modulation provided by theintelligent power generation management controller of an embodiment ofthe present invention; and

FIG. 6 is a simplified schematic diagram illustrating componentplacement in an over-the-road vehicle in accordance with one embodimentof the present invention.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates, in simplified block diagrammatic form, an embodimentof an air conditioning system of particular applicability to anover-the-road or off-road commercial vehicle. Unlike conventionalvehicle air conditioning systems, the system 10 of the present inventionutilizes a brushless DC motor 12 to drive a variable speed compressor14. This variable speed, brushless DC motor-driven compressor 14circulates refrigerant through a refrigerant-to-liquid orrefrigerant-to-air heat exchanger 16 to an optional refrigerant receiverand dryer 18. The refrigerant then passes through an expansion device 20and a refrigerant-to-air heat exchanger 22 to cool the passengercompartment.

In one embodiment of the present invention, a secondary parallel coolantloop is provided through expansion device 24 and refrigerant-to-air heatexchanger 26. Such secondary, parallel coolant loops are often used todirectly cool the sleeping compartment of an over-the-road vehicle'scab. As such, the heat exchanger 26 is typically smaller than the heatexchanger 22 as the volume for which it is responsible is reducedcompared to the primary driver/passenger compartment of the cab. Whilenot illustrated in FIG. 1, the two refrigerant coolant loops may beselectively coupled via a valve. The inclusion of such a valve allows,for example, only the sleeping compartment to be air conditioned when nooccupant is in the main passenger compartment of the cab and vise versato increase the efficiency of the system. The refrigerant then passesthrough an operational refrigerant accumulator 28 before being returnedto the compressor 14.

By utilizing a variable speed compressor 14 driven by brushless DC motor12, the vehicle's air conditioning system may be operated during bothengine on and engine off (no idle) conditions. The provision of thevariable speed compressor 14 also allows the system to operate at alower capacity during engine off operation to conserve the amount ofstored energy available for usage by the system from the vehicle'sbatteries 34. The control for this operation is provided by anintelligent power generation management controller 30 that monitorsvarious system parameters and the availability of power sources on thevehicle.

In this way, the vehicle's air conditioning system is now capable ofbeing powered by either the vehicle's main electric power generationsystem 32, which is available while the vehicle's engine is operating,or by the electrical system while the engine is off by utilizing thestored electric power in the battery storage system 34. Additionally,the intelligent power generation management controller 30 also has thecapability utilizing shore power 36 or power from an auxiliary electricpower unit 38, such as a genset or fuel cell.

In the system 10 of the present invention, the use of the electricdriven compressor 14 provides the ability to modulate its output fromfull capacity to low capacity. This allows the use of a single airconditioning system that can be used for both high load on-roadoperations with the engine operating, and at a lower capacity with theengine off to continue to cool the passenger compartments. Coordinationof this modulation is provided by the intelligent power generationcontroller 30, which reduces the speed of the compressor when lowercapacity power sources are only available. This modulation extends theduration of available operation from such power sources. That is, with areduced speed of the compressor, the electric power demand is reduced aswell.

As illustrated in FIG. 2, an alternate embodiment of the system of thepresent invention includes a high pressure coolant loop 46 and a lowpressure coolant loop 40 in a full HVAC system. The high pressurecoolant loop 46 is driven by the compressor 14, and may be constructedas a modular, sealed refrigeration power cell having fixed tubing withpermanent connections. The low pressure coolant loop 40 utilizes a lowpressure coolant pump 42 to circulate the low pressure coolant through arefrigerant-to-liquid heat exchanger 44 that serves as the heat exchangemedium between the high pressure coolant loop 46 and this secondary loop40. Such a configuration is described in U.S. Pat. No. 6,276,161,entitled Modular Low Pressure Delivery Vehicle Air Conditioning System,assigned to the assignee of the instant application, the disclosure andteachings of which are hereby incorporated in their entireties byreference thereto. In such a configuration, the primary high pressurecoolant loop 46 may be manufactured as a single integrated module havingfixed tubing and permanent connections between the components thereof.As described in the above-identified patent, such a configurationminimizes the possibility of refrigerant leaks through high pressurecouplings.

As illustrated in FIG. 2, the secondary low pressure coolant loop 40uses a treated liquid-to-air heat exchanger 48 located within thevehicle's interior to provide cooling to the passenger compartments. Toprovide heating of the vehicle passenger compartments a coolant heater50 may be utilized in the secondary low pressure coolant loop 40. Duringsuch heating operation, the intelligent power generation managementcontroller 30 need only operate the secondary loop coolant pump 42 andthe coolant heater 50 to provide this functionality. That is, no powerneed be delivered to the variable speed motor driven compressor 14 inthis mode of operation, thereby further reducing the power consumptionduring engine off operation and extending the period of time that suchoperation is available.

In an alternate embodiment illustrated in FIG. 3, an air heater 52 maybe provided in the air outlet duct 54 of the vehicle HVAC system. Thismay be a fuel fired heater (FFH) or a resistance-type heater. In thisconfiguration, the intelligent power generation management controller 30need not operate either the high pressure loop or the low pressurecoolant loop, but instead only operate a circulation fan 56 and the airheater 52 to provide the necessary heating for the vehicle passengercompartments. This configuration provides additional power consumptionsavings and allows for a longer duration operation of the system in theheating mode. In the cooling mode of operation, the compressor will beoperated to circulate refrigerant through the high pressure refrigerantto air or low pressure liquid to air heat exchanger 58. A mode doorand/or temperature control door 60 controls the flow of air through theduct 54 to regulate the temperature of the air flowing into the vehiclepassenger compartments as is known in the art.

As discussed briefly above and as illustrated in FIG. 4, the system ofthe present invention utilizes an intelligent power generationmanagement controller 30 to modulate the speed, and therefore thecapacity, of the variable speed brushless DC motor driven compressor 14.This output control can modulate the compressor 14 between a maximumcompressor speed and capacity 62 during, for example, engine onoperation or operation with an unlimited input power source such as thevehicle electrical power generation system 32 or a shore powerelectrical system 36, and a minimum compressor speed and capacity 64during, for example, periods of operation utilizing limited sources ofelectrical power such as the electric power battery storage system 34 oran electrical auxiliary power unit power system 38. Operation at anyspeed and capacity between these two points 62, 64 is available ascontrolled by the intelligent power generation management controller 30.This controller 30 may also vary the modulation of compressor 14 whenadditional or different sources of power become available and as systemparameters change to maintain optimal system performance.

For example, the controller 30 may operate the compressor 14 at maximumcompressor speed and capacity while the vehicle is being driven tomaintain the temperature of the passenger compartment of the vehicle ata user selected temperature. As the vehicle is parked and the engine isturned off, the controller 30 will sense the loss of the vehicleelectric power generation system 32 and will begin to utilize electricpower from the electric power battery storage system 34 to drive thecompressor. The controller 30 will then reduce the compressor speed andcapacity so as to not draw an excessive amount of power from thebattery. The speed and capacity of the compressor may be increased asneeds demand as determined by the controller 30. However, the controller30 will not allow an amount of power to be discharged from the batterystorage system 34 that would result in an insufficient amount of powerremaining available to start the vehicle, or not allow an amount ofpower to be discharged from the battery storage system that will reducethe life of the system. As such a point is neared, the controller 30will disable the power output to the compressor 14 thereby shutting downthe HVAC system until and unless an additional source of power becomesavailable or the batteries are recharged. In one embodiment, this pointis set at approximately 11.5 volts DC under load, although other setpoints may be appropriate based on the starting needs of the engine andbattery life.

While the system is operating from the battery storage system 34, if thevehicle is connected to a shore power electrical system 36 thecontroller 30 will sense the availability of this new power source. Thecontroller 30 will then begin utilizing this source to the exclusion ofthe battery system 34, and will increase the compressor speed andcapacity as needed to maintain the temperature of the interior. If,instead, an auxiliary power unit on the vehicle is started, intelligentpower generation management controller 30 will switch to this source ofpower to drive the compressor 14 to the exclusion of the battery storagesystem 34, and will increase the modulation of the compressor 14 asneeded. However, unlike when the system is operated from the vehicleelectric power generation system 32 or from the shore power electricsystem 36, the controller 30 may well reduce the modulation of thecompressor 14 based upon the power draw and capacity of the APU powersystem 38. That is, the controller 30 recognizes that the APU powersystem 38 and the battery storage system 34 are limited resources thatmay be needed for other functions on the vehicle. As such, thecontroller 34 will ensure the conservation of some portion of theseresources by disabling the HVAC system prior to exhaustion of thesepower sources.

As illustrated in FIG. 5, the intelligent power generation managementcontroller 30 monitor various system parameters to perform itsmodulation control function. Both the exterior ambient temperature 66and the vehicle's interior ambient temperature 68 are monitored by thecontroller 30 to determine a compressor capacity to achieve and maintainthe interior set point temperature. Typically, the larger the differencebetween the exterior and interior temperatures, the higher the capacityneeded to maintain the differential. As the exterior ambient temperature66 drops or the vehicle interior ambient temperature set point 68 risesthe controller 30 may reduce the compressor speed and capacity and stillmaintain the user selected interior temperature.

The controller 30 also monitors the compressor power consumption 70 andthe total system power consumption 72 in its modulation of thecompressor speed and capacity. This information is used by thecontroller 30 to modulate the compressor 14 to ensure that the availablepower sources are not depleted beyond a predetermined power capacity forthose times that a limited power source is being utilized. Thecontroller 30 can reduce the compressor speed and capacity if themonitored power consumption exceeds appropriate levels. These parametersare also utilized to provide system protection from over load faults.

The controller 30 also monitors system parameters of the refrigerationsystem including the compressor speed 74 and the refrigerant systempressures and temperatures 76. The compressor speed signal 74 isutilized in the closed loop proportional, integral, derivative (PID)control of the compressor modulation. The refrigerant system pressuresand/or temperatures are utilized as control parameters to regulate thecompressor speed and capacity so that the power utilization isoptimized. That is, the compressor modulation may be reduced once atemperature has been reached within the system to adequately cool theinterior passenger compartments. Indeed, the compressor may be stoppedaltogether while the heat exchanger that cools the passengercompartments is at a temperature sufficient to provide adequate cooling.Once the temperature of this heat exchanger rises above a levelsufficient to provide adequate cooling, the controller 30 may once againstart the compressor 14 to reduce this temperature. In this way, thedraw from the available power sources is minimized while still achievingthe goal of providing adequate passenger cooling with the limited powersources available to drive the system. The system parameters alsoprovide the controller 30 with the ability to detect faults within thesystem that reduce its ability to cool the interior compartment and thatincrease its power consumption.

System status display and control inputs may be provided between thecontroller 30 and the operator via a user input/output display 78 withinthe passenger compartment. When such a display 78 is utilized,communication of control parameters from the user may be provided to thecontroller 30 by means of a serial data link. Likewise, the display ofsystem control and status information may be provided by the controller30 to the display 78 by this serial data link. Control parameters fromthe user will typically include the desired operating mode of the HVACsystem including off, heat, and cool modes of operation. Likewise atemperature setting may also be input through this I/O device 78.

In one embodiment of the present invention, the user may also selectwhich of the available power sources should be utilized to drive thevariable speed compressor. The controller 30 may also provide switchingbetween available power sources as a source is depleted, or may querythe user for authorization before providing such automatic source powertransfer. Fan speed and interior compartment selection may also becontrolled via the user I/O display or controls 78. System statusinformation may also be displayed on the user I/O display 78 includinginterior and exterior temperatures, fan speed, mode selection, remainingavailable power, selected power source, available power sources, statusand warning messages, etc.

In one embodiment of the present invention, the system allows adjustmentof the following parameters via the display/control 78: compressorminimum control output; compressor maximum control output; maximumcurrent draw; indoor unit minimum speed output; battery cutout voltage;compressor cooling control parameters kp, ki, and kd; and indoor fanheating control parameters Kp, Ki, and Kd. These parameters provide theproportional, integral, and derivative, or rate gains for the controlPID equations. In this embodiment, the following parameters are reportedto the display 78: operating mode; set temperature; cab temperature;discharge air temperature; battery voltage; battery current; andcompressor commanded speed.

During operation, the intelligent power generation and managementcontroller 30 processes the user inputs to determine the operationalmode of the HVAC system. When the heating mode of operation is commandedby a user in the engine off (no idle) condition, the controller 30commands a heater, e.g. coolant heater 50 illustrated in FIG. 2 or airheater 52 illustrated in FIG. 3, to turn on. These heaters may be fuelfired heaters or electric resistance heaters as appropriate. Thecontroller 30 also controls the interior fan speed via a pulse widthmodulated (PWM) PID control loop in order to maintain the interior cabtemperature at the set point. If, however, the user selects a coolingmode of operation, the condenser fan and pump outputs are turned on andthe interior compartment fan is set to 100%. Initially, the compressorspeed is set to the minimum capacity and speed setting. The controller30 then modulates the speed and capacity of the compressor 14 tomaintain the cab temperature at the user define set point via the PIDcontrol, except when certain conditions are encountered. Theseconditions include a high current/high load limit that reduces thecompressor speed if the supply current exceeds a predefined currentlimit. In one embodiment, this current limit is set at 40 amps.

Similarly, if the requested compressor speed is at a minimum and thedischarge air temperature is below the temperature set point, thecompressor speed is set to zero, until the discharge air temperature isabove the set point for more than a predetermined amount of time.Further, if the pressure sensing indicates a fault within therefrigeration the requested compressor speed will also be set to zero.The compressor will be disabled for a predetermined period of timebefore the compressor is allowed to be operated. Finally, if the batteryvoltage drops below a predetermined value load the controller 30 willdisable all outputs until power has been cycled to the controller 30 oran alternate source of power becomes available.

While the system of the present invention provides significantadvantages when integrated into a vehicle's HVAC system, many currentlyexisting vehicles that already have a HVAC system installed would alsobenefit from such a system. However, the cost of removing a vehicle'scurrent HVAC system and reinstalling the system of the present inventionmay well be cost prohibitive. Therefore, in an alternate embodiment ofthe present invention the components of the system are modularized forinstallation on a vehicle in addition to the currently existing HVACsystem that is operable only during engine on operation. With thisembodiment, the passenger compartment temperature may be controlledwithout running the engine.

Such a system installation is illustrated in exemplary locations in FIG.6. As may be seen from this FIG. 6, the system 10 is provided a sealedrefrigeration system with the variable speed brushless DC compressor andintegrated coolant heater. This sealed unit may be installed in variouslocations within the interior or exterior of the vehicle. In FIG. 6, theinstallation of the sealed module is illustrated as being external tothe engine and passenger compartments. Within the passenger compartmentan inside HVAC unit 80 including a heat exchanger and fan is installedto provide the air conditioning of the passenger compartment. Thisinterior unit 80 may also include an air heater if a coolant heater isnot included with sealed system 10. In this embodiment the intelligentpower generation management controller 30 is also installed within thepassenger compartment. Through this controller 30 the users may controlthe system of the present invention and receive read out information.

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the preciseembodiments disclosed. Numerous modifications or variations are possiblein light of the above teachings. The embodiments discussed were chosenand described to provide the best illustration of the principles of theinvention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

1. A method of operating an air conditioning system for a vehicle havingan engine to provide air conditioning to a sleeping area of the vehiclehaving an electric power generation and storage system, comprising thesteps of: drawing electric power from the electric power generation andstorage system when the engine is operating to drive an electricallydriven, variable-speed compressor to cool the vehicle; drawing electricpower from the electric power generation and storage system when theengine is not operating to drive the electrically driven, variable-speedcompressor to cool the vehicle; disabling operation of the electricallydriven, variable-speed compressor when an output of the electric powergeneration and storage system drops below a threshold; and determining astarting power requirement threshold of the vehicle's engine, andwherein the step of disabling operation of the electrically driven,variable-speed compressor when the output of the electric powergeneration and storage system drops below the threshold comprises thestep of disabling operation of the electrically driven, variable-speedcompressor before the output voltage of the electric power storagesystem drops below the starting power requirement threshold of thevehicle's engine.
 2. The method of claim 1, further comprising the stepof varying a speed of the electrically driven, variable-speedcompressor.
 3. The method of claim 2, wherein the step of varying thespeed of the electrically driven, variable-speed compressor comprisesthe step of increasing the speed of the electrically driven,variable-speed compressor based on an increased demand for cooling. 4.The method of claim 2, wherein the step of varying the speed of theelectrically driven, variable-speed compressor comprises the step ofdecreasing the speed of the electrically driven, variable-speedcompressor based on a decreased demand for cooling.
 5. The method ofclaim 1, further comprising the steps of monitoring at least one of anexterior ambient temperature and an interior ambient temperature of thevehicle, and varying a speed of the electrically driven, variable-speedcompressor to achieve an interior set point temperature.
 6. The methodof claim 1, wherein the step of disabling operation of the electricallydriven, variable-speed compressor when an output of the electric powergeneration and storage system drops below a threshold further comprisesthe step of monitoring a voltage of the electric power generation andstorage system.
 7. The method of claim 1, wherein the step of disablingoperation of the electrically driven, variable-speed compressor when anoutput of the electric power generation and storage system drops below athreshold further comprises the step of monitoring a power consumptionfrom the electric power generation and storage system.
 8. The method ofclaim 1, further comprising the step of modulating a speed of theelectrically driven, variable-speed compressor based on whether thevehicle engine is on or off.
 9. A method of operating an airconditioning system for a vehicle to provide air conditioning to asleeping area of the vehicle having an electric power storage system,comprising the steps of: drawing electric power from the electric powerstorage system when an engine of the vehicle is not operating to drivean electrically driven compressor to cool the vehicle; and disablingoperation of the electrically driven compressor when an output of theelectric power storage system drops below a threshold; wherein theelectric power storage system is also used to start the vehicle'sengine, and wherein the step of disabling operation of the electricallydriven compressor when the output of the electric power storage systemdrops below a threshold comprises the steps of determining a startingpower requirement threshold of the vehicle's engine and disablingoperation of the electrically driven compressor when the output of theelectric power storage system reaches the starting power requirementthreshold of the vehicle's engine.
 10. The method of claim 9, whereinthe electric power storage system includes at least one battery, furthercomprising the step of charging the at least one battery from anelectric power generation system of the vehicle when the engine isoperating.
 11. The method of claim 10, further comprising the step ofdrawing electric power from the electric power generation system whenthe engine of the vehicle is operating to drive the electrically drivencompressor to cool the vehicle.